Rocket propellant igniter



May 24, 1960 B. R. ADELMAN 2,937,493

ROCKET PROPELLANT IGNITER Filed Feb. 28, 1955 FIG. 2.

INVENTOR. B.R.ADELMAN BY #W M ATTORNEYS ROCKET PROPELLANT IGNITER BarnetR. Adelman, Waco, Tex., assignor to Phillips Petroleum Company, acorporation of Delaware Filed Feb. 28, 1955, Ser. No. 490,760

5 Claims. (Cl. 60'-35.6)

This invention relates to the ignition of a solid rocket propellant. Inone of its aspects it relates to *an improved method and apparatus forthe ignition of an' internal-external burning propellant grain.

Solid propellant grains arev formed in a variety of shapes and sizessuch as cylinders, boards and tubes. The tubular propellant grains areusually burned on the inside and the outside simultaneously with onlythe end's'being restricted. With the increased burning area provided inthis configuration of propellant charge, ignition of the entire surfacehas been diflicult to obtain and it is desirable that the entire exposedsurface be ignited in orderfor United StatcsPatent o" Recently it hasbeen discovered that superior solid propellant mixtures are obtainedcomprising a major proportion of a solid oxidant such as ammoniumnitrate or ammonium perchlorate and a minor proportion of a rubb nf derma e ial such a a. cop l m of a conjugated diene and a vinylpyridine orother substituted heterocyclic nitrogen base compound, which afterincorporation is cured by a quaternization reaction or a vulcanizationreaction. Solid propellant mixtures of this nature and a process fortheir production are disclosed and claimed in copending applicationSerial No. 284,447, filed April 25, 1952, by W. B. Reynolds and J. E.Pritchard.

The difficulty encountered in the ignition of an internalexternalburning charge is in obtaining uniform ignition ofthe periphery of thecharge. This difiiculty does not occur in the case of an externalburning charge because the gases are forced to pass over the peripheryof the charge because there is no other place for the hot gases to go.This is also true in the case of an internal burning charge. It isdifferent, however, in the case of an internal-external burning chargebecause the gases tend to pass through the center opening rather than totake the more devious path around the periphery of the charge.

It is an object of this invention to provide an improved method for theignition of an internal-external burning propellant grain.

It is also an object of this invention to provide an improved igniterfor the ignition of an internal-external burning propellant grain.

It is an object of this invention to provide an igniter which is capableof directing hot gases and burning particles over the entire area of aninternal-external burning propellant grain so as to provideinstantaneous ignition of the entire exposed area of the propellantgrain.

It is a further object of this invention to provide a rocket motorutilizing an internal-external propellant 2,937,493 Patented May 24,196i) ice.

tained.

Other and further objects and advantages will be apparent to one skilledin the art upon study of the following description of the inventionincluding the attached drawing wherein:

Figure l is a schematic sectional elevation of a rocket motorillustrating a preferred embodiment of the invention, and

Figure 2 is a sectional elevation of a rocket motor illustrating amodification of the invention.

Broadly speaking, the invention provides an igniter comprising acylindrical cup having positioned therein a conical cup whose open baseis substantially parallel to the opening of the cylindrical cup. Bothcups aresub stantially filled with an easily ignitable material such asblack powder, or a suitable pyrotechnic .composition' The igniter ispositioned in the combustion chamber, spaced from one end of thepropellant charge and centrally located with respect to the crosssectional dimensions of the combustion chamber so that upon ignition thecone shaped cup directs hot gases and burning particles down through thecenter opening of the propellant grain and the cone shaped configurationof'the inner cup deflects burning particles and hot gases evolved fromthe cylindrical cup so that these burning particles and hot gases passover and around the outside of the propellant place the rocket motor ishermetically sealed by the die:

phragm so as to avoid deterioration of the propellant charge and in thesecond place the diaphragm seals combustion gases in the combustionchamber, upon ignition, so that optimum operation pressure is quicklyattained. Pressure favors the combustion rate of a propellant chargecomprising ammonium nitrate and a rubbery binder material. Therefore,the sealed combustion chamber attains maximum rate of combustion almostimmediately when ignition is obtained.

Referring now to the drawing and particularly to Figure 1, a rocketmotor is comprised of casing 10 having exhaust nozzle 11 positioned atone end and closure member 12 attached to the other end by threadedconnection 13. Tubular propellant charge 14 is positioned in combustionchamber 15 and maintained in position by compression springs 16operating against shoulders 17. The charge is restricted at each end byplates 18 and 19 and centrally positioned by spiders 21 and 22 which areprojections from plates 18 and 19. Frangible disk 23 acts as a closurefor exhaust nozzle 11 and also supports igniter 24 comprised ofcylindrical cup 25 and conical 'cup 26. Ignition wire 27 is imbedded inigniter 24 and connected to a circuit containing a source of electricalpotential (not shown). Cylindrical igniter cup 25 and conical ignitercup 26 are made from light material, preferably fusible metal, plasticmaterial or paper material such as cardboard.

In Figure 2 is shown a modification of the rocketmotor of Figure 1 andlike numerals refer to like members whenever possible. In thismodification exhaust nozzle 11 is secured to casing 10 by threadedconnection 13a. Igniter 24 is secured to the closed end portion 12a.Spring 16a is shown as a single compression spring, however, a pluralityof smaller springs can be employed as in Figure 1.

In both Figures 1 and 2 the conical cup 26 is adapted so as to deflectburning particles and hot gases from cylindrical cup 25 around theperiphery of the tubular propellant grain 14 and at the same time todirect buming particles and hot gases through the center opening ofpropellant grain 14.

It is preferred that the hollow solid angle of the conical cup be suchthat the inner conical surface of rotation confining the ignitionproducts of the ignited material from the outer cylindrical cup has adiameter substantially equal to or slightly less than the diameter ofthe end of the grain at the point of intersection with the grain. Inmost cases the intervening distance between the igniter cup and the endof the grain is fixed and the hollow solid angle of the cup isconstructed accordingly, however, it is possible to vary the distance atwhich the igniter cup is placed from the grain in order to achieve thedesired result.

Reasonable variations and modifications are possible within the scope ofthe disclosure of the present invention, the essence of which is theprovision of an igniter for a tubular solid rocket grain comprising acontainer substantially filled with ignition material and havingpositioned therein deflecting means adapted so as to direct a portion ofthe ignition products to the periphery of the grain and to direct aportion of the ignition products to the perforation of the grain.

That which is claimed is:

1. An igniter for an internal-external burning propellant graincomprising a cylindrical container means having one open end and beingsubstantially filled with an ignition material; means embedded in saidigniter material in said container and adapted to direct a portion ofignition products to the internal surface of said grain and theremaining portion of ignition products to the external surface of saidgrain; and means for igniting said ignition material.

2. An igniter for an internal-external burning propellant grain whichcomprises a cylindrical cup member; a conical cup member positioned insaid cylindrical cup with its open base substantially parallel with thecylindrical cup opening; an easily ignitable material substantiallyfilling both of said cups; and means to simultaneously ignite thematerial in both cups.

3. In a rocket motor comprising a combustion chamher having an exhaustnozzle, an internal-external burning propellant positioned in saidcombustion chamber, exhaust nozzle closure means closing said nozzle andadapted so as to fail at less than combustion chamber operatingpressure, the improvement comprising a propellant igniter positioned insaid combustion chamber comprising a cylindrical cup spaced from saidpropellant with the open end of said cup facing said propellant, aconical cup positioned in said cylindrical cup with its open basesubstantially parallel with the open end of said cylindrical cup, aneasily ignitable material substantially filling both of said cups; andmeans for igniting said propellant igniter.

4. In a rocket motor comprising a combustion chamber having an exhaustnozzle and an internal-external burning propellant comprising ammoniumnitrate oxidant, conjugated diene-vinylpyridine copolymer binder, and aburning rate catalyst, positioned in said combustion chamber, theimprovement comprising an igniter comprising a cylindrical cup, aconical cup positioned in said cylindrical cup so that the open base ofsaid conical cup is substantially parallel with the open end of saidcylindrical cup, both of said cups being substantially filled with aneasily ignitable material, said igniter being positioned in saidcombustion chamber with the open ends of said cups facing saidpropellant and spaced from said propellant so that the conical surfaceof rotation defining a projection of the hollow solid angle of theconical cup has a diameter substantially equal to the diameter of thepropellant at the point of intersection with the propellant; and meansfor igniting said igniter.

5. An igniter for an internal-external burning propellant grain whichcomprises a cylindrical cup member; a conical, fusible material cupmember positioned within the cylindrical cup member and having a hollowsolid angle such that a projection of the inner conical surface ofrotation of said angle has a diameter substantially equal to thediameter of the propellant grain at the point of intersection with thepropellant grain; an easily ignitible material substantially fillingboth of said cups; and means to simultaneously ignite the material inboth cups.

References Cited in the file of this patent UNITED STATES PATENTS2,685,837 Sage et a1. Aug. 10, 1954 who

